1. Field of the Invention
The present invention relates to a uniaxial drive unit using a pulse drive motor and, more particularly, to a uniaxial drive unit capable of carrying out fine feed.
2.Description of the Related Art
Conventionally, there has been known a uniaxial drive unit (referred also to as a linear motion type unit) which is made up of a fixed table and a moving table which is supported so as to be slidable in uniaxial direction with respect to the fixed table and is driven in this direction. Most of the uniaxial drive units of this type are driven by a motor of any type (for example, a pulse drive motor such as a stepping motor and a linear motor).
FIG. 5 is a perspective view showing one example of the uniaxial drive unit. In FIG. 5, a uniaxial drive unit 1 has a fixed table 2, a moving table 4 which is supported on sliding faces 3, 3 so as to be slidable in the uniaxial direction (the arrow-marked directions in FIG. 5) with respect to the fixed table 2, and a motor driving mechanism 5.
In the uniaxial drive unit 1, a screw member 6 of the motor driving mechanism 5 is fixed to the fixed table 2 via bearings 7, 7 so as to be rotatable, and a nut member, not shown, engaging with the screw member 6 is fixed to the moving table 4.
By driving a motor 8 fixed to the fixed table 2, the motor 8 being one element of the motor driving mechanism 5, the moving table 4 integral with the nut member is moved back and forth in the arrow-marked directions in FIG. 5.
As a motor used for such a uniaxial drive unit, unlike the motor shown in FIG. 5, a linear motor that is nonrotatable can also be applied. Of the linear motors, a linear motor having a fixed part, which is a rod-shaped magnet, and a moving part, which is a ring-shaped member fitted on the fixed part, having a coil member, and being capable of moving linearly along the fixed part, has features of less cogging, less unevenness of speed, and the like, and hence has been coming onto the market (for example, trade name: SHAFT MOTOR, manufactured by GMC HILLSTONE Co., Ltd.).
FIG. 6 schematically shows a cross section of such a linear motor 101. A moving part 104, which is a ring-shaped member having a coil member, is fitted on a fixed part 102, which is a rod-shaped magnet in which the N poles and the S poles are arranged alternately in a linear form. Due to the interaction between the magnetic flux of the fixed part 102 and the electric current flowing in the coil member of the moving part 104, the moving part 104 moves linearly along the fixed part 102 in accordance with Fleming's left-hand rule. The coil member of the moving part 104 is supplied with an electric current by a driving circuit, not shown.
As an improved technology for such a linear motor, a linear motor capable of operating steadily with high accuracy has been proposed (for example, see Japanese Patent Laid-Open Nos. 8-331834 and 11-150973).
The uniaxial drive unit has a joystick at an operating part, and is driven manually from low speed to high speed according to the tilt angle of the joystick.
When the moving table is driven by the above-described joystick operation, a high-speed or medium-speed operation has no problem. On the other hand, when a low-speed operation is performed, the operation must be performed by tilting the joystick through a minute angle or by switching the operation to a step feed operation. However, since the maximum tilt angle of joystick is generally small, it is difficult for the operator to carry out tiltable control of minute angle, so that it is difficult to provide fine feed to the moving table.
Also, there is known the uniaxial drive unit in which in the case of a screw feed mechanism as shown in FIG. 5, a manual knob for fine feed is connected to the screw member via a deceleration mechanism, and fine feed is provided to the moving table by manually turning the manual knob. However, the manual knob turns at the time of electrical feed, which entails a danger.